Method of forming paper containing gaseous filled spheres of thermoplastic resins and paper thereof



United States Patent METHOD OF FORMING PAPER CONTAINING GASEOUS FILLED SPHERES F THERMO- PLASTIC RESINS AND PAPER THEREOF Duane L. Kenaga and Ralph M. Gooch, Midland, Mich, assignors to The Dow Chemical Company, Midland, Mich, a corporation of Delaware No Drawing. Filed Apr. 3, 1964, Ser. No. 357,288 Claims. (Cl. 162168) This invention relates to an improved paper. It more partcularly relates to an improved paper containing small plastic particules.

Paper has many uses in packaging, printing, preparation of containers, and the like. One of the basic shortcomings of conventional paper is its weight. The relatively high density of paper imposes a significant financial burden in shipping, mailing, and the like. For example, magazines, when printed on a paper which is sufliciently dense and thick to give the reader the impression of quality, weighs considerably more than is necessary if the minimum thickness of paper were used which would permit readability. Frequently among the thicker papers, often referred to as paperboard or boxboard, a relatively high weight is required to obtain a desired thickness and stiltness. In many instances, such as in the preparation of paper cups, present papers do not have a sufficient insulating value for use as hot cups unless an excessive quantity of pulp is employed.

It is an object of this invention to provide an improved paper having a low density and improved opacity per unit weight.

A further object of this invention is to provide an improved paper having a relatively high stiifness per unit weight.

Another object of this invention is to provide an improved paper which has low thermal conductivity per unit weight.

Still another object of the invention is to maintain tear strength while lowering the basis weight.

These benefits and other advantages in accordance with the present invention are achieved in the preparation of a paper by incorporating therein a plurality of synthetic resinous particles having a generally spherical shape and defining a generally concentric spherical cavity therein. Papers in accordance with the present invention are most readily prepared by the addition of from about 0.05-60 percent of hollow generally spherical particles by weight based upon the weight of the dry pulp, to the pulp slurry. Generally such plastic particles range in diameter from about one-half to about 200 microns in diameter. However, desirably such particles have diameters ranging from about 3 to about 50 microns and most advantageously have particle diameters of from about 5 to about 20 microns. Generally such particles have bulk density ranging from about 0.2 to 3 pounds per cubic foot Oftentimes such particles are commercially available and are made from glass, phenolic plastics and urea formaldehyde. Most advantageously and beneficially such particles are prepared from thermoplastic resinous materials rather than thermosetting materials. The thermoplastic resinous materials generally are less brittle and are readily manipulated with a minimum breakage and can be prepared from polymers of widely differing ice physical properties. Such small hollow particles are prepared by the limited coalescence polymerization technique utilizing a polymerizable monomer and a volatile blowing agent, the blowing agent exhibiting limited solubility in the polymer. A typical preparation of such particles is as follows:

A polymerization reactor equipped with an agitator was charged with parts of deionized water and 15 parts of a 30 weight percent colloidal silica dispersion in water. The colloidal silica dispersion was 30 weight percent solids and available under the trade name of Ludox HS. To this mixture was added 2.5 parts of a 10 weight percent aqueous solution of a copolymer prepared from diethanol amine and adipic acid in equimolar proportions by carrying out a condensation reaction to give a product having a viscosity of about 100 centipoises at 25 centigrade. One part of a solution containing 2.5 weight percent potassium dichromate was added. The pH of the aqueous solution was adjusted to 4 with hydrochloric acid. Methyl methacrylate was utilized :as the monomer. An oil .ph-ase mixture was prepared utilizing 100 parts of methyl methacrylate and containing 20 weight percent neopentane (27.6 volume percent based on the total volume of the monomer-neopentane mixture) and 0.1 part of benzoyl peroxide as a catalyst. The oil phase mixture was added to the water phase with violent agitation supplied by a blade rotating at a speed of about 10,000 r.p.m. The reactor was immediately sealed and a portion sampled to determine the particle size. The droplets appeared to have diameters of from about 2 to about 10 microns. After the initial dispersion, the reaction mixtures was maintained at a temperature of about 80 centigrade for a period of 24 hours. At the end of this period, the temperature was lowered and the reaction mixture had the appearance of a white, milky liquid similar to a chalk-white milk. A portion of the mixture was filtered to remove the particles and the particles or beads subsequently dried in an air oven at the temperature of about 30 centigrade. A portion of the dried spherical particles were heated in an air oven at a temperature of centigrade for about 3 minutes. Upon heating, the particles showed a marked increase in volume. Microscopic examination of the particles prior to foaming indicated particles having diameters of from about 2 to about 10 microns and having disposed therein a distinct spherical zone which appeared to contain liquid and a small vapor space. The particles which had been heated were examined microscopically and were found to have diameters of from about 2 to 5 times the diameter of the original particle and to have a relatively thin, transparent wall and a gaseous center, i.e., a monocell.

By utilizing the principles of limited coalescence, a wide variety of expanded plastic particles may be attained.

These expanded particles are spherical in shape and have a concentric spherical cavity. The hollow spherical particles are readily incorporated into a paper pulp by admixture with the wet pulp prior to deposition on the Fourdrinier screen or on the collecting surface of a cylinder machine. Depending upon the particular surface characteristics of the thermoplastic resinous particle, it may be necessary to incorporate a coagulant or retention aid into the pulp slurry to assure that a major portion of the plastic particles are deposited on the surface of the pulp fibers and are not carried away by the white water.

Generally the plastic particles are utilized in a paper in concentrations of from about 0.05-60 percent by weight depending upon the desired characteristics of the resultant paper. If papers of minimum bulk density are desired, a maximum quantity of particles are incorporated therein. If maximum physical strength is desired, generally lower quantities are used. Beneficially the incorporation of from about 5-15 percent by weight of such plastic particles is oftentimes sufficient to reduce the density of a paper sufficiently to provide a significant decrease in the cost of mailing of a finished printed article such as a magazine or a book. Yet all of the required physical characteristics of the paper are retained. The particles or microspheres employed in the present invention are readily incorporated in either long fiber or short fiber pulps, and also in ground wood pulps and rag pulps. The incorporation of the plastic particles provides on an equal basis weight comparison a significant increase in the stiffness of the paper as well as a significant increase in the caliper. Thus, it makes possible the prepa ration of papers having greater stiffness, lighter weight, and having increased caliper, all desirable features for many books, magazines, and the like.

The following experiments serve to illustrate the benefits and advantages of the present invention and employ the following terms:

Freeness of pulp is a measure of the rate of flow of water through the pulp and is measured in accordance in accord with that described in the Tappi Standard Forming Hand Sheets for Physical Tests of Pulp T205 m-58. Hand sheets were prepared by beating the pulp to the desired degree of freeness and subsequently adding the hollow particulate particles to the pulp slurry and transferring the slurry to the deckel box and subsequently draining the water from the deckel box after any obvious movement of the slurry had ceased. The hand sheet was formed on an mesh screen and subsequently dried by the following procedure. The hand sheet and screen are removed from the deckel box, the sheet pressed against and transferred to a sheet of blotting paper. The sheet was then placed against a polished chromium plated sheet under a pressure of about 60 pounds per square inch for a sufficient length of time to remove by capillary action the majority of water available thereto. The sheet of blotting paper is removed and replaced with a half inch felt. The felt-paper-plated sheet sandwich is placed in a platen press between closed platens for a period of 4 minutes. The platen adjacent the plated sheet was heated to a temperature of centigrade. The hand sheet was then removed from the press and sandwiched and conditioned for 24 hours at a temperature of 73 centigrade under a relative humidity of 50 percent before testing. The experimental data obtained from the experiments are set forth in the following tables, wherein the microspheres are polymethyl methacrylate prepared in the manner hereinabove described.

TABLE I A +10% Mierospheres Cato 8 +10% Microsph'eres Control 0.5% A 0.75% A 1% Cato 8 3% Gate 8 Basis Weight, gnL/m. 70. 3 57. 6 57. 6 57. 6 57. 6 57. 6 Percent; Microsphcres Ret w 3. 0 2. 9 3. 7 4. 1 Bulk, ccJgm 1. 28 1. 38 1. 56 1. 62 1. 55 1. 57 Caliper in inches 0. 0035 0. 0031 0. 0037 O 0038 0. 0038 O. 0039 Tappi Opacity, percent 86.8 78.8 87.6 89. 2 88. 6 88. 9 Brightness, Rm 0. 027 0. 620 0. 689 0. 691 0. 9 0. 688 Burst Factor. 35. 8 30. 3 2S. 7 26. 8 27. 6 27. 8 Tensile, length to brea 6, 330 6, 560 6, 5, 750 6, 090 6, 400 Tensile, p.s.i 6, 100 6, 350 5, 390 4, 770 5, 5, Tear Factor 69. 7 48. 5 60.7 50.8 54.9 02. 5 M.I.T. Fold 27 35 64 90 73 280 l A-A eopolymer of 80 parts acrylonitrile and 20 parts by weight 2-aminoethyl methacrylat-e. 2 Cato 8-A cationic starch manufactured by National Starch Company.

with the Tappi Standard T227 m-58, also referred to as the Canadian Standard Freeness.

Stiffness of the paper or sheets is measured in accordance with the Tappi Standard T489 m-60. Ring crush refers to the Ring crush test of paperboard in accordance with the Tappi Standard T472 m-51. The Pick test is designed to test the surface strength of paper performed in accordance with Tappi test T459 m48. The equipment employed for forming hand sheets was generally Opacity is measured in accordance with Tappi Standards T425 m60 with the exception that a wave length of 560 millimicrons was used. Burst factor was deter mined in accordance with Tappi Standard T403 m-53; the length to break is the length in meters of a sheet of paper sufficient to cause the paper to rupture. The tear factor was determined by Tappi Standard T414 m-49. The MIT. fold was determined in accordance with Tappi Standard T423 m-SO.

Control+3% Alum 2 10% Microspheres+ Mydel 550 +3% Alum +10% 0.5% 0.75% Micro- Mydel 550 Mydel 550 spheres Basis weight, g./m. 70. 3 57. 6 57. 6 57.6 57. 6 Percent Microspheres Retained 3.1 3. 7 4. 3 Bulk, ce./gm 1. 40 1. 61 1. 61 1. 04 Caliper in inches 0. 0036 0. 0032 0. 0037 0. 0039 0. 0040 Tappi Opacity, percent- 86.4 79.2 86.8 87.8 87.8 Brightness, R a, 0. 638 0. 030 O. 688 0. 697 0. 097 Burst Factor 34.9 26.1 23. 31. 5 26. 7 Tensile, length to break- 6, 340 6, 580 5, 570 5, 830 6,100 Tensile, p.s.i 6, 400 6, 400 4, 530 4, 820 4, 850 Tear Factor 68. 49. 9 63. 5 64. 56. 9

1 Mydel 550 a copolymer of acrylamide and acrylic acid. 2 Aluminum Sulphate A1z(SO4)318H3O.

TABLE III Un- Alum 0.5% Rosin-l-Alnm treated Control 3% A1n.ml-A* Control 3% Control A* 11* Basis Weight, corrected to grams/sq. meter 41.6 41. 6 41. 6 41.6 41. 6 41.6 Microsphcres Added, percent 5 10 5 10 Analysis of Microsphcres y Pyrolysis 1.1 2.1 1.0 2. 2 Bulk, cc./gms. (Average) 2.00 2. 24 2.00 2.14 2. 20 Caliper, (Average) inches. .0034 .0039 0033 0037 .0039 Dry Burst Factor 10. 1 9. 7 9. 4 8. 9 8. 3 Tappi Opacity, percent 76. 2 81. 3 76.0 79.0 81. 1 Brightness, R w 743 767 743 772 770 Tensile, length to break 3, 400 3, 000 3, 400 3, 200 3, 100 Tear Factor 82 92 78 89 90 M.I.T. Fold 4. 5 3. 8 4. 5 3. 8 4.0 Tensile, lbs/sq. in 2, 400 1, 900 2,400 2, 100 2, 000 M. of E. x 1,000 300 240 320 280 260 Norm-A", See Table V.

TABLE IV [0.5% Rosin-l-Alum] Control A* i A* I 13* B" C* C" 0* Control Basis Weight, Corrected to grams/sq. meter 41.6 41. 6 41.6 41. 6 41. 6 41. 6 41. 6 41.6 41.6 Microsphcres Added, percent 5 1O 5 2. 5 5 10 A alysis of Microsphcres by Pyrolysis 0 1.0 2.2 1. 4 2. 7 0. 4 1.0 2. 0 0 Bulk, cc./gm. (Avg) 2. 00 2.14 2. 20 2.18 2. 62 1.95 2.18 2.15 1. 88 Caliper, (Avg) inches 0033 0037 0039 0038 0046 0033 0037 0037 0032 Dry Burst Factor 9. 4 8. 9 8.3 9. 6 8. 4 9. 9 9. 6 9. 7 10. 6 'Tappi Opacity, percent" 76.0 79. 0 81. 1 74. 8 75.9 74. 1 77.0 75.4 73.6 Brightness, R w .743 772 .770 .738 746 .733 .744 .739 732 Tensile, Length to Break 3, 400 3,200 3, 100 3,400 2, 800 Tear Factor: 78 89 9O 83 92 M.I.T. Fold 4. 5 3.8 4.0 4.0 Tens le. Pounds per sq. inch. 2, 400 2, 100 2, 000 2, 200 1, 500 M. 01 E. x 1,000 320 28 260 290 200 No'rE.A", B, 0*, See Table V.

TABLE V.PHYSICAL PROPERTIES OF MICROSPHERES Diameter in Microns Mlcrosphere Batch Bulk Density Small Average Large cent by weight bleached kraft. The furnish was beaten to a Canadian Standard freeness of 300 milliliters. After beating one-half of one percent by weight based on the dry weight of the furnish of a rosin size was added. The pH of the resultant slurry was 6.2 which Was subsequently adjusted to a pH of 4.5 by means of sulphuric acid in the stock and machine chests. During operation, the pH at the fan pump varied between 5.1 and 5.5. A slurry in water of hollow plastic particles having a diameter of from about 7 microns to about 110 microns was prepared and metered into the recycle water going to the fan pump. The paper machine was placed in operation without the addition of the hollow plastic particles. After operating for a period of time the quantity of plastic spheres added to the stock was varied. The results are set forth in the following tables.

TABLE VI Microsphcres Added 0 Initial Final Control Control 2. 7% 4. 6% 10. 2% 12. 1%

Basis Weight, corrected to gram/sq. meter 41.6 41.6 41.6 41.6 41.6 41.6 Analysis of Microsphcres by Pyrolysis 0 0. 5 1. 1 1. 7 2. 3 0 Bulk ccJgm. (Average) 2. 2. 48 2. 52 2. 2. 71 2. 33 Dry Burst Factor" 7. 2 6.9 6. 1 5. 8 5. 4 7.0 Tappi Opacity, pe 76. 2 77.5 76. 7 78.7 78. 2 76.1 Brightness, Rec 712 .719 .721 724 724 718 Tensile, length of hrea e direction-.. 2, 900 3,000 2, 600 2, 400 2, 200 3, Tensile, length to break Cross Machine direction 2, 200 2, 200 2, 100 1, 900 1, 800 2, 000

Tear Factor, Machin 45 45 47 46 44 47 Tear Factor, Cross Machine direction 47 47 49 49 45 47 M.I.T. Fold (0.5 Kg.), Machine direction 38 31 23 20 15 41 M.I.T. Fold (0.5 Kg), Cross Machine direction. 22 17 14 13 14 13 Tensile lbs/sq. in., Machine direction 1, 700 1, 700 1, 500 1, 300 1, 100 1, 900 Tensile lbs/sq. in., Cross Machine direction... 1, 300 1,200 1, 200 1, 000 900 1,200

TABLE VIL-K AND N INK TEST, PERCENT DROP IN BRIGHTNESS Percent Microspheres Added Initial Final Control Control 2.7 4.6 10.1 12.1

Condition 1 52 52 53 52 52 52 Condition 2 49 48 50 48 50 49 Condition 3- 35 36 38 38 37 38 Condition 4 21 29 26 28 32 38 IGT PICK, 2# INK, FEET/MINUTE Condition 1 328 353 530 370 348 325 Condition 2- 180 140 188 198 205 193 Condition 3 358 273 243 283 293 310 Condition 4 473 405 353 388 325 278 Condition 1=Uncoated, unsupercalendered sample.

Condition 2=Uncoated, supercalendered 6 nips. Condition 3=Coated, with coating color Number 1, supered 6 n ps. Condition 4=Coated, with coating color Number 2, supered 6 nips.

By way of further illustration, a plurality of hand sheets alum was added and the pH adjusted to 5.2 by means of 'were prepared in a manner hereinbefore described utiliz- 30 N 10 NQOH- ing a 1:1 mixture of bleached groundwood pulp and an unbleached spruce sulfite pulp beaten to a Canadian Standard freeness of 157 milliliters; the hand sheets were made up to a basis Weight of about 120 grams per square meter. Three percent by weight based on the weight of the pulp of The plastic spheres are identified by the following designations: A at a bulk density of 3.4 pounds per cubic foot; D at a density of .5 pound per square cubic foot; E at a density of about .7 pound per cubic foot and F at at a density of about .9 pound per square foot. The results are set forth in the following tables.

TABLE VIII Treatment Control 5% A 10% A 5% E 10% E Percent Miscrospheres Retained 2.4 5.0 1 2.2 5.4 Basis Weight, g./m. 118. 4 124. 5 128. 7 125. 6 128. 7 Caliper, inches" 0. 0070 0. 0082 0. 0093 0. 0109 0. 0152 Bulk, cc./gm 1. 51 1. 66 1. 84 2. 19 3. Percent increase over control 1o 22 45 99 Taber Stiffness 1. 09 1. 44 1. 83 2. 28 4.03 Percent increase over control- 30. 3 67. 9 109. 2 269. 7 Gurley Stifiness 1. 79 2. 25 3.12 3. 84 6. 22 Percent increase over controL- 25.7 74. 9 114. 247. 5 Ring Crush, 50, Relative Humi 24. 19 25. 68 31. 19 38. 08 Percent increase over controL. 11. 4 18. 3 43. 7 75. 4 Ring Crush, high, Humidity 18. 19 21.01 21. 89 24. 86 Percent increase over control 9. 9 26. 9 32. 3 50. 2 Modulus oi Elasticity X 4 46. 6 39. 9 31. 4 20. 2 Tensile, p.s.i 3, 997 3, 401 2,869 1, 966 Tensile, breaking length, 4, 667 4, 338 4, 422 3, 934

E =polymethyl methacrylate spheres to microns average diameter and having a bulk density of 0.6 pound per cubic foot.

TABLE IX Treatment Control 5% A 10% A 5% E 10% E Stiflness calculated from M.O.E.

(X10 D=EI. Where I=bh 12 (h=caliper) 159 214 267 339 591 Percent increase over control 68 113 272 Stifiness calculated on basis of state ment that stifiness increases as square of caliper at constant weight. 2.22 2. 3. 88 7. 16 Percent increase over control 24 51 117 360 Gurley stiffness, direct reading. 2. 25 31. 2 3. 84 6. 22 Percent increase over control... 25. 7 74. 9 114. 5 247. 5 Taber stillness, direct reading. 1. 44 1. 83 2. 23 4. 03 Percent increase over control 30. 3 67. 9 109. 2 269. 7

A plurality of hand sheets were prepared generally in accordance with the foregoing procedures utilizing a spruce gronndwood pulp which was beaten to a Canadian Standard Freeness of 121 milliliters. The slurry was treated with 2 percent by weight alum based on the dry 10 Weight alum based on the weight of the pulp was added to the slurry. A pH was adjusted between and 5.5 and vary quantities of expanded polymethyl methacrylate microspheres having a bulk density of 0.829 pound per cubic 5 weight of the pulp and the pH of the resultant slurry adfoot w added to Pulp slurry lmmedlately to justed to about A plurality of ontrol sheets were formation of the hand Sheets. The rfisults are set forth prepared varying in weight in order that comparison might in the following table.

TABLE XI Alum Percent Microspheres I Control Percent Microspheres added 0 2 4 6 3 g 10 Percent Retention ofMierospheres 0 0.8 1.6 2 4 41g 4. 7 Bulk, ee m. average 1. 36 1. 43 1. 1.60 1. '72 1. Caliper, average inches 0.0127 0.0132 0. 0141 0.0154 0.0167 0. 0185 Basis Weight, gmsJsq. meter 237 234 240 244 246 254 Tensile, lbs/Sq. inch 1- 5, 660 5, 860 5, 250 4, 800 4, 580 4, 270 Tensile, Breaking length, meters 5, 400 5,870 5, 520 5, 390 5, 540 5, 550 Modulus of Elasticityxlmuu 583 574 512 451 402 349 Ring Crush, lbs 119 122 116 112 111 Gurley'Stifl'ness (corrected to 1 x 3 sample). 5, 5,030 6,180 6, 490 7,130 8, 910 Percent Increase over control 2 21 2 39 75 be made with two different samples of microspheres having densities of 0.418 and 0.829 pound per cubic foot re- A plurality of hand sheets were prepared in a manner similar to the foregoing illustration with the exception spectively. The results are set forth in the following that bleached kraft was employed as the pulp and was table. 30 beaten to a Canadian Standard Freeness of 400 milliliters.

TABLE X Percent Microspheres Wax Pick Weight, Caliper Gurley Tensile Density lbs/ L gin/1n. Inches Stifi'ness p.s.i.

Added Retained 1 No Complete Rupture Rupture 0 0 143 0. 0093 2. 03 17. 8 7A 9A 0 0 156 o. 0098 2. 83 20. 8 0 0 0. 0104 a. 47 22. 1 8A 11A 0 0 0. 0111 4. 23 23. 0 0 0 0. 0113 4. 85 25. 3 8A 11A 0 0 196 0. 0117 5. 78 26.6 0 0 207 0. 0130 7. 15 27. 1 9A 11A 2. 0 0. 8 146 0. 0102 2. 8o 18. 7 4. 0 1.9 144 0. 0116 3. 48 17.0 6. 0 2. 8 149 0. 0127 4. 00 18. 9 6A 8A 8. 0 3. 6 148 0. 0136 4. 58 17. 2 10.0 4. 2 156 0.0150 5. 60 16. 5 5A 7A 2. 0 1. 0 145 0. 0102 2. 92 18. 8 4. 0 2. 0 148 0. 0123 4.13 18. 4 0. 0 3. 1 152 0. 0137 4. 85 16. 2 7A 9A 8. 0 4. 1 153 0. 0150 5. 75 17. 9 10. 0 5. 8 155 0. 0171 6. 75 16. 3 6A 7A A plurality of hand sheets were prepared in a manner generally similar to the foregoing illustration wherein a Polymethyl methacrylate microspheres having diameters of from about 3 to about 130 microns (number average southern pine unbleached kraft pulp was beaten to a Cana- 55 20) and a bulk density of 0.82 pound per cubic foot were diaii Standard Freeness of 485 milliliters. Two percent by employed. The results are set forth in the following table.

TABLE XII Percent 13 Basis Wt. Bulk ce./g. Burst Gurley Tcmp. C.2 Caliper Added g./m. Factor Stiffness Reached mils.

3 2% alum added in each case.

4 17.4% retained (30/130=24% added) 72% retention.

Hand sheets were prepared in :accordance with the hereinbefore delineated procedure wherein microspheres of various compositions were employed. The microspheres were added at levels of and parts by weight per 100 parts by weight fiber together with two percent by weight alum. The results are set forth in the following table.

merely illustrative and is not to be construed or interpreted as being restrictive or otherwise limiting of the present invention, excepting as it is set forth and defined in the hereto appended claims.

What is claimed is:

1. A paper comprising paper making fibers having incorporated therein a plurality of synthetic resinous ther- TABLE XIII Microspheres used Composition Basis Bulk Burst Gurley Iemp. Caliper Wt. g./m. ccJg. Factor Stifiness Reached mils.

v Alum control 157. 3 I 1. 47 10s 1, 370 so 9.1 }Methylmethacrylate (Avg. d1a. 2O 1111cr0ns, bulk 154.1 1.62 116 1, 980 77 9. 8 densit 0.82 lbs/cu. 112.). 141. s 1. 99 102 1, 980 74 11.1 95/5 methylmethacrylatelacrylonitrlle (Avg. die. 161. 3 2.02 109 2, 590 73 12. 8 13 microns, bulk density 0.25 lbs/cu. 13.). 157.8 2. 85 91 4, 820 t 3 17. 7 70/30 styrene/acrylonitrile (Avg. dia. microns, 153.8 1. 70 116 2, 110 77 10.3 H bulk density 2.21bs./cu. a. 165. 9 2.14 95 3,600 71 1 1.0 }10/30 styrene/acrylomtnle (Avg. dia. 27 microns, 160. 7 2. O4 87 2, 590 72 12. 9 bulk density 1.1 lbs/cu. it. 187 5, 490 65 17. 7 11 1, 400 79 9. 0 }Methylmethacrylate (Avg. (1121. 3 mlcrons) 151 4 L 42 u g 1 270 79 6 1 After one minute on hot plate, surface temp, 86 C. Two percent by weight alum (based on pulp) used in all cases.

In a manner similar to the foregoing illustrations other papers having generally commensurate benefits are prepared which contain expanded hollow plastic particles of a copolymer of 80 weight percent methyl methacrylate,

and 20 weight percent styrene; 90 weight percent methyl methacrylate, 10 weight percent ortho-chloro styrene; 70

weight percent methyl methacrylate, 30 weight percent orthochlorostyrene; 50 weight percent methyl methacrylate, 50 weight percent ortho-chlorostyrene; 10 Weight percent methyl methacrylate, 90 weight percent orthochlor-ostyrene; polyortho-chlorostyrene; polyvinylbenzyl chloride; 70 weight percent acrylonitrile, 30 weight percent vinylidene chloride; equal portions of acrylonitrile and vinylidene chloride; 90 weight percent methyl methacrylate, 10 weight percent acrylonitrile; 50 weight percent methyl methacrylate, 50 weight percent acrylonitrile; 70 weight percent methyl methacrylate, 30 percent by weight para-tert.-butyl styrene; 80 weight percent methyl methacrylate, 20 weight percent vinyl acetate; 90 weight percent methyl methacrylate, 10 weight percent butyl acrylate; 98 weight percent styrene, 2 weight percent 'methacrylic acid; 83 weight percent styrene, 2. weight percent methacrylic acid and 15 weight percent of vinylbenzyl chloride; 91 weight percent vinylidene chloride, 9 weight percent acrylonitrile; and the like.

Papers prepared in accordance with the invention employing thermoplastic resinous particles emboss readily with relatively low pressure. Exceptionally desirable embossed papers are obtained wherein the embossed area of the paper is embossed at a temperature about or above the softening temperature of the plastic particles.

As is apparent from the foregoing specification, the method and manufacture of the present invention are susceptible of being embodied with various alterations and modifications which may difier particularly from those that have been described in the preceding specification and description. For this reason, it is to be fully understood that all of the foregoi g intended to be moplastic particles, each of the synthetic resinous particles having a generally spherical shape and defining a generally spherical gaseous space therein, the synthetic resinous particles being present in a proportion from about 0.5 to about 60 percent by weight of the weight of the paper making fibers in the paper and each of the resinous particles having a diameter of from about 0.5 to about 200 microns.

2. The paper of claim 1 wherein the thermoplastic resinous particles have a diameter of from about 3 to about 50 microns.

3. The paper of claim 1 wherein the thermoplastic particles are polymethyl methacrylate.

4. In a method for making paper which comprises depositing paper making fibers upon a screen from an aqueous suspension and subsequentlydrying and compressing the deposited fibers to form a generally continuous sheet, the improvement which comprises incorporating within the aqueous suspension from which the fibers are deposited a plurality of synthetic resinous particles, each particle having a generally spherical shape and defining a generally spherical gaseous space therein and retaining in theresultant fibrous sheet at least a portion of the synthetic resinous thermoplastic particles, the resinous particles being present in a proportion of from about 0.5 to about 60 percent by weight of the weight of the paper making fibers and each of the particles having a diameter of from about 0.5 to about 200 microns.

5. The method of claim 4 wherein the thermoplastic particles are polymethyl methacrylate.

References Cited by the Examiner UNITED STATES PATENTS 2,972,554 2/ 1961 Muskat et al. 260-25 X 3,037,903 6/1962 Baurnan et al l62l0l X 3,067,482 12/ 1962 Hollowell 2602.5 X 3,137,631 6/1964 Soloway. 3,210,239 10/1965 Eberl et al. 162-101 X FOREIGN PATENTS 497,154 8/ 1950 Belgium.

DONALL H. SYLVESTER, Primary Examiner.

S. LEON BASHORE, Examiner, 

1. A PAPER COMPRISING PAPER MAKING FIBERS HAVING INCORPORATED THEREIN A PLURALITY OF SYNTHETIC RESINOUS THERMOPLASTIC PARTICLES, EACH OF THE SYNTHETIC RESINOUS PARTICLES HAVING A GENERALLY SPHERICAL SHAPE AND DEFINING A GENERALLY SPHERICAL GASEOUS SPACE THEREIN, THE SYNTHETIC RESINOUS PARTICLES BEING PRESENT IN A PROPORTION FROM ABOUT 0.5 TO ABOUT 60 PERCENT BY WEIGHT OF THE WEIGHT OF THE PAPER MAKING FIBERS IN THE PAPER AND EACH OF THE RESINOUS PARTICLES HAVING A DIAMETER OF FROM ABOUT 0.5 TO ABOUT 200 MICRONS. 